So great convention overall. May write up my own review separately.
But I digress...
I too used to volunteer for a few big conventions in the UK and have seem quite a few different takes on the "queuing to see your favorite person"
One that may be of use to the more popular creators is a managed and timed line... So only "X" amount of people can physically queue, everyone else is given an incremental numbered slip, When your number is less than the number on display (Increment by one with every attendee seen, or multiples to ease micro) you can join the queue.
This: -
A: Forces people to go do other stuff,
B: Keeps the lines manageable.
C : Gives staff the ability to cut off attendance to a guest so they can have breaks
This system has been used successfully with A-List celebrity's and queues of thousands... So a few hundred for a couple internet personality's should be fine. XD
Another suggestion, prohibit photos.... I know I know.... But I just mean at the meet and greet, have a separate time slot for a proper photo shoot, use your own gear and email the pictures across
(The trade off from losing the selfie is the attendee gets a much better photo!)
And lastly, as stated before. More staff... But again I worked as a Gopher so I know it can be difficult to get the numbers in.